Field of the Invention
The invention relates to a method for determining the fault location of a fault on a line of an electrical energy supply network in which first current and voltage values are measured at a first line end of the line, second current and voltage values are measured at a second line end of the line and the location of the fault is defined using the first and second current and voltage values following the occurrence of a fault on the line.
The invention also relates to a corresponding device and a system for determining the fault location of a fault on a line of an electrical energy supply network.
The safe operation of electrical energy supply networks requires the fast and reliable detection and shutdown of any faults, such as, for example, short circuits or grounding faults. Causes of faults which result in a shutdown may, for example, be lightning strikes, torn or otherwise damaged lines, defective insulations in cable lines or the unwanted contact of overhead lines with animal or plant parts. In order to shorten fault-related downtimes, faults of this type must be localized as accurately as possible in order to enable an elimination by a maintenance team of the fault cause and any consequential damage caused by the fault.
In the simplest, but also most expensive, case, a fault is located by means of visual inspection. The maintenance team passes along the defective line and examines it for visible fault points. This procedure is slow and prone to error.
A different procedure has therefore largely been adopted, whereby the fault location at which the fault on the line is located is isolated by way of an analysis of measurement values, e.g. currents and voltages measured during the fault occurrence. A plurality of different methods have since become known for this purpose, the accuracy of which impacts significantly on the maintenance cost of the energy supply network. Great importance is therefore attached to improving the accuracy of the algorithms used for the fault location in order to simplify the maintenance and, in particular, shorten fault-related downtimes of the energy supply network.
A rough result of the fault location can be achieved, for example, by identifying the fault direction. This method is used primarily in compensated, isolated and high-impedance-grounded energy supply networks with a radial structure or a low degree of meshing. A wattmetric method, for example, can be used, as known from the European Patent EP 2 476 002 B1. A different method for detecting the fault direction is the “wiper relay principle” which is known in one possible embodiment, for example, from the international patent application WO 2012/126526 A1. However, an additional evaluation is necessary in these methods for more accurate fault location.
Methods for more accurate fault location use, for example, the measured current and voltage signals of the fundamental wave (50 Hz or 60 Hz signals) for fault location. Here, methods are known which use measured values of only one of the line ends (unilateral fault location) or measured values of both line ends (bilateral fault location). As a result, the fault location is normally indicated as the distance from the respective measuring point (as a percentage of the line or in km or miles).
In the case of the use of measured values of only one line end, the cost of performing the fault location is low. This fault location method is primarily an impedance-based method in which an impedance through to the fault location is calculated from current and voltage measured values. The fault location can be inferred through comparison with the line impedance of the entire line in the fault-free case. An example embodiment of a fault location method of this type can be found, for example, in U.S. Pat. No. 4,996,624.
The accuracy of this method depends, inter alia, heavily on the measurement accuracy of the current and voltage transformers that are used, the accuracy of the line parameters used for the fault location (e.g. impedance per unit length) and on the given fault conditions (e.g. fault resistance, load) and the network characteristics. Faults and the transient responses in the current and voltage signals can have a negative impact on the accuracy of this method. The resulting measurement errors may amount to several percent.
An improved accuracy in the fault location can be achieved through the use of measured values from both line ends. Here, the fault-location-related measured values must be collated via a suitable communication connection. In this context, reference is made to U.S. Pat. No. 5,929,642; in the method described there, a fairly high accuracy (measurement error approximately 1-2%) is achieved in the fault location using current and voltage measured values from both line ends by means of estimation methods and non-linear optimization methods.
Whereas the accuracy of the fault location in the case of impedance-based fault location methods depends on the measurement accuracy of the measuring transformers that are used and the network characteristics, a broad independence from these values can be achieved through the use of a fault location method according to the “traveling wave fault location” principle. According to this principle, the transient signal components produced in the event of a fault and occurring in the form of “traveling waves” are taken into consideration for the fault location instead of the measured current and voltage signals. Here, the high-frequency traveling wave edges are measured and are provided with a timestamp. Since the propagation speed of the traveling waves is approximately equal to the speed of light, the fault can be accurately located from the evaluation of the timestam ping. Accuracies in the range of a few dozen meters can be achieved with this fault location method. An example of a fault location method of this type can be found in U.S. Pat. No. 8,655,609 B2. However, in the known method, a high-precision temporal synchronization between the measuring devices at both line ends must be provided so that uniform timestamps can be allocated. Receivers, for example, of a satellite-based time pulse (e.g. a GPS signal) are necessary here for providing a time signal that is synchronous at both ends.